Method for producing alkyl carboxylates by multi-stage esteridication interrupted with a dehydration step

ABSTRACT

Method for producing an alkyl carboxylate, in which a carboxylic acid and an alcohol are esterified by reaction in the presence of an acid catalyst, by removing water in a dehydration step established halfway in the esterification reaction using a solid acid catalyst as the acid catalyst, and restarting the esterification reaction to complete the esterification reaction.

TECHNICAL FIELD

The present invention relates to a method for producing an alkylcarboxylate from a carboxylic acid and an alcohol. The present inventionis especially suitable for producing an alkanedioic acid dialkyl esterusing an alkanedioic acid as the carboxylic acid, and the alkanoedioicacid dialkyl ester can be suitably used as an intermediate product ofdrugs, agricultural chemicals, perfumes, dyes, liquid crystal materials,high molecular materials, etc.

BACKGROUND ARTS

As a method for producing an alkanedioic acid dialkyl ester in thepresence of an acid catalyst, it is known to esterify an alkanedioicacid and a monohydric alcohol in the presence of sulfuric acid (JapanesePatent Laid-Open (Kokai) No. 63-243060). Furthermore, as a method forproducing an ester using a solid acid catalyst, it is known to esterifya carboxylic acid and an alcohol using an ion exchange resin as acatalyst (Japanese Patent Laid-Open (Kokai) No. 63-297340).

However, according to the production method of Japanese Patent Laid-Open(Kokai) No. 63-243060, the gross yield of the alkanedioic acid dialkylester is as low as about 85 to 95% and the purity is as low as about 90to 98%. Furthermore, the isolation and purification of the producedalkanedioic acid dialkyl ester requires a step of neutralizing the acidcatalyst by an alkali and a step of distillation in a high vacuum ofabout 13 to 53 Pa (0.1 to 0.4 Torr) in a high temperature range of 117°C. to 201° C., and the method does not allow a highly pure alkanedioicacid dialkyl ester to be obtained economically at a high yield.

DISCLOSURE OF THE INVENTION

The inventors studied intensively to solve these problems, and as aresult, found that an alkanedioic acid dialkyl ester can be obtained ata high purity of 99% or more with the amount of the alcohol used keptsmaller, by removing the water produced in the reaction system in adehydration step established halfway in the esterification reaction andrestarting the esterification reaction, to complete the esterificationreaction.

Furthermore, they found that if a solid acid catalyst is used as theacid catalyst, the produced alkanedioic acid dialkyl ester can be easilyseparated from the acid catalyst. Thus, the present invention has beencompleted.

The present invention is a method for producing an alkyl carboxylate, inwhich a carboxylic acid and a monohydric alcohol are esterified byreaction in the presence of an acid catalyst, comprising the steps ofremoving the reaction solution from contact with the acid catalyst andremoving the water produced in the reaction system in a dehydration stepestablished halfway in the esterification reaction, with the reactionsolution kept away from contact with the acid catalyst, and restartingthe esterification reaction, in the presence of the acid catalyst tocomplete the esterification reaction.

THE MOST PREFERRED EMBODIMENTS OF THE INVENTION

In the present invention, it is preferable to conduct the dehydrationstep when the reaction solution is kept away from contact with the acidcatalyst. If the dehydration step is established with the reactionsolution kept in contact with the acid catalyst, an ester hydrolyzingreaction may occur and this will lower the ester yield.

In the present invention, the method for keeping the reaction solutionaway from contact with the catalyst halfway in the esterificationreaction is not especially limited. Neutralization or filtration, etc.can be used.

In the present invention, the number of dehydration steps established inthe esterification reaction is not especially limited, but it ispreferable that the number of dehydration steps is 1 to 3 in view ofworking efficiency. If the number of dehydration steps is 4 or more, theworking efficiency tends to decline.

In the present invention, as for the timing of the aforementioneddehydration step or steps established in the esterification reaction,when the number of dehydration steps established halfway in theesterification reaction is one, the time when the conversion of thealkanedioic acid into the alkanedioic acid dialkyl ester has become 85to 95%, especially 90 to 94% is preferable for decreasing the amount ofthe alcohol used. Thus, the dehydration step takes place partway throughthe reaction but not necessarily halfway.

In the present invention, the dehydration method in the dehydration stepis not especially limited, and can include distilling away under reducedpressure, separation, centrifugation, or contact with a dehydratingagent such as a molecular sieve or magnesium sulfate, etc.

In the present invention, as for the degree of dehydration in thedehydration step, it is preferable to dehydrate until the water contentof the reaction mixture becomes 0.5% or less, especially 0.1% or lesswhen the esterification reaction is restarted, since the amount of thealcohol used can accordingly be kept smaller.

The acid catalyst used in the present invention is preferably a solidacid catalyst. The solid acid catalysts which can be used here includesilica gel, alumina, zeolite, heteropoly-acids, weak acid ion exchangeresins and strong acid ion exchange resins. Especially strong acid ionexchange resins are preferable.

Strong acid ion exchange resins especially preferably used in thepresent invention are benzenesulfonic acid type ion exchange resins.Such strong acid ion exchange resins include, though not limited to,"Diaion" SK series, trade name, produced by Mitsubishi Kagaku, "Diaion"PK series, trade name, produced by Mitsubishi Kagaku, "Amberlite"IR-120B, trade name, produced by Organo, "Amberlist" 15E, trade name,produced by Organo, "Dowex" 50W series, trade name, produced by DowChemical, etc. Among them, preferable are "Diaion" PK series, andespecially preferable is "Diaion" PK-220-H. These strong acid ionexchange resins can also be used as a mixture.

The strong acid ion exchange resins preferably used in the presentinvention can be regenerated, as required, by interaction with a mineralacid such as sulfuric acid, hydrochloric acid or nitric acid.

The carboxylic acids which can be preferably used in the presentinvention are alkanedioic acids represented by the general formulaHOOC--X--COOH (where X stands for a straight chain, branched chain orcyclic alkyl chain with 6 to 14 carbon atoms). Such alkanedioic acidsinclude straight chain alkanedioic cids such as octanedioic acid,nonanedioic acid, decanedioic acid, undecanedioic acid, dodecanedioicacid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acidand hexadecanedioic acid; branched chain alkanedioic acids such asmethyloctanedioic acid, ethyloctanedioic acid, methylnonanedioic acid,ethylnonanedioic acid, methyldecanedioic acid, ethyldecanedioic acid,methylundecanedioic acid, ethylundecanedioic acid, methyldodecanedioicacid, ethyldodecanedioic acid, methyltridecanedioic acid,ethyltridecanedioic acid, methyltetradecanedioic acid,ethyltetradecanedioic acid and methylpentadecanedioic acid; andcycloalkanedicarboxylic acids such as cyclobutanediacetic acid,cyclohexanedicarboxylic acid, cyclohexanediacetic acid andbicyclohexanedicarboxylic acid. Among them, preferable are decanedioicacid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid andtetradecanedioic acid.

It is preferable that the monohydric alcohol used in the presentinvention is a straight chain or branched chain monohydric alcohol with1 to 4 carbon atoms. Such preferable monohydric alcohols includemethanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,2-methyl-1-propanol and 2-methyl-2-propanol. Among them, more preferableare methanol and ethanol.

The reaction temperature of the present invention is usually 50 to 100°C., but a range of 60 to 80° C. is preferable. If the reactiontemperature is lower than 50° C., the reaction does not proceedsufficiently to lower the yield. If the reaction temperature exceeds100° C., the acid catalyst may be inactivated.

The reaction pressure of the present invention can be changed in a rangeof 0.05 to 0.5 MPa (0.5 to 5 atmospheric pressure), but a range of 0.1to 0.2 MPa (1 to 2 atmospheric pressure) is preferable.

The reaction of the present invention can be effected by the batchmethod or the flow method.

When the reaction of the present invention is effected by the batchmethod, the ratio of the weight of the alkanedioic acid:the weight ofthe monohydric alcohol:the volume of the acid catalyst depends on thenumber of dehydration steps established in the esterification reaction,their timings and the final yield of the alkanedioic acid dialkyl ester.If only one dehydration step is established halfway in theesterification reaction at a point where the conversion into thealkanedioic acid dialkyl ester reaches 93%, to achieve a finalalkanedioic acid dialkyl ester yield of 99%, it is preferable that theratio of the weight of the alkanedioic acid:the weight of the monohydricalcohol:the volume of the acid catalyst in the first step of reaction isin a range of 1:(0.8-4):(0.5-10) [g/ml], and that the ratio of theweight of the alkanedioic acid:the weight of the monohydric alcohol:thevolume of the acid catalyst in the second step of reaction is in a rangeof 1:(0.8-2):(0.5-10) [g/ml]. If the amount of the monohydric alcohol issmaller than the above range, the yield of the alkanedioic acid dialkylester is too low, and if larger than the above range, the excessiveamount of the monohydric alcohol must be removed when the alkanedioicacid dialkyl ester is purified, to require a longer time and largerequipment. If the amount of the acid catalyst is smaller than the aboverange, the reaction progresses so slowly as to lower the yield of thealkanedioic acid dialkyl ester, and if larger than the above range, theamount of the alkanedioic acid dialkyl ester produced per unit amount ofcatalyst declines inefficiently.

It is more preferable that the ratio of the weight of the alkanedioicacid:the weight of the monohydric alcohol:the volume of the acidcatalyst in the first step of the reaction is in a range of1:(1-2):(2-5) [g/ml] and that the ratio of the weight of the alkanedioicacid:the weight of the monohydric alcohol:the volume of the acidcatalyst in the second step of the reaction is in a range of1:(1-1.5):(1-3) [g/ml].

When the reaction of the present invention is effected according to theflow method, the ratio by weight of the alkanoic diacid : the monohydricalcohol depends on the number of dehydration steps to be establishedduring the esterification reaction, their timings and the finalalkanedioic acid dialkyl ester yield. If only one dehydration step isestablished in the esterification reaction at a point where theconversion into the alkanedioic acid dialkyl ester reaches 93%, toachieve a final alkanedioic acid dialkyl ester yield of 99%, it ispreferable that the ratio by weight of the alkanedioic acid:themonohydric alcohol in the first step of reaction is in a range of1:(2-4), and that the ratio by weight of the alkanedioic acid:themonohydric alcohol in the second step of the reaction is in a range of1:(0.8-2). In this case, the SV value showing the amount of reactionsolution flow depends on the ratio by weight of the alkanedioic acid tothe monohydric alcohol, but it is preferable that SV is in a range of0.3 to 0.8/h in both the first and second steps of the reaction. If theamount of the monohydric alcohol is smaller than the above range, theyield of the alkanedioic acid dialkyl ester declines, and the solubilityof the alkanedioic acid becomes so low as to make the execution of theflow method difficult. If it is larger than the above range, anexcessive amount of the monohydric alcohol must be removed when thealkanedioic acid dialkyl ester is purified, requiring a longer time andlarger equipment. If the SV value is larger than the above range, thereaction does not proceed sufficiently to lower the yield, and if the SVvalue is smaller than the above range, the amount of the alkanedioicacid dialkyl ester produced per unit of time becomes smallinefficiently.

It is more preferable that the ratio by weight of the alkanedioicacid:the monohydric alcohol in the first step of the reaction is in arange of 1:(3-4), and that the ratio by weight of the alkanedioicacid:the monohydric alcohol in the second step of the reaction is in arange of 1:(1-1.2). It is more preferable that the SV value is in arange of 0.4 to 0.6/h in both the first and second steps of thereaction.

When the reaction of the present invention is effected according to thebatch method, the solid acid catalyst can be separated by filtrationafter completion of the esterification reaction, and from the obtainedfiltrate, the unreactive monohydric alcohol and produced water can bedistilled away at atmospheric pressure or under reduced pressure, toisolate the alkanedioic acid dialkyl ester.

When the reaction of the present invention is effected according to theflow method, the unreactive monohydric alcohol and produced water can bedistilled away at atmospheric pressure or under reduced pressure from areaction solution which has passed through a solid acid catalyst tank,to isolate the alkanedioic acid dialkyl ester.

The alkanedioic acid dialkyl esters obtained in the present inventioncan be suitably used as intermediates of drugs, agricultural chemicals,perfumes, dyes, liquid crystal materials, high molecular materials,etc., and typically preferably used as raw materials for obtaining largecyclic lactones used for perfumes.

EXAMPLES

The present invention is described below concretely in reference toexamples of the present invention and comparative examples, but is notlimited thereto or thereby.

Example 1

Marketed ion exchange resin "Diaion" PK-220 was regenerated into theacid type by 2N hydrochloric acid.

A 200 ml three-neck flask with a reflux condenser was charged with 10 gof dodecanedioic acid, 10 g of methanol and 20 ml of the regenerated"Diaion" PK-220, and the mixture was stirred by a mechanical stirrer,while being refluxed (64° C.) for 6 hours. The reaction solution wasanalyzed by gas chromatography, and it was found that the conversion ofdodecanedioic acid into dodecanedioic acid dimethyl ester was 90.12%.The reaction solution was filtered, and the obtained filtrate wasconcentrated under reduced pressure by a rotary evaporator, to obtain11.10 g of a residue as a colorless solid. The water content of theresidue was 0.1%.

The residue thus obtained was put into a 200 ml three-neck flask with areflux condenser, together with 10 g of methanol and 20 ml of thereproduced PK-220, and the mixture was stirred by a mechanical stirrer,while being refluxed (64° C.) for 6 hours. The reaction solution wasanalyzed by gas chromatography, and it was found that the conversionfrom dodecanedioic acid into dodecanedioic acid dimethyl ester was99.23%. The reaction solution was filtered, and the obtained filtratewas concentrated under reduced pressure by a rotary evaporator, anddried by a vacuum dryer for 4 hours, to obtain 11.22 g of a residue as acolorless solid. The residue was analyzed by gas chromatography, and itwas found that the purity of dodecanedioic acid dimethyl ester was99.19%. The yield of dodecanedioic acid dimethyl ester obtained from thepurity was 99.20%.

Example 2

A stainless steel tube with a diameter of 12 mm and a length of 200 mmopen at both the ends was packed with 17 ml of the "Diaion" PK-220reproduced as described in Example 1, and placed in a 60° C.thermostatic oven.

A solution with 10 g of dodecanedioic acid dissolved in 40 g of methanolwas passed through said stainless steel tube by a fixed delivery pump ata rate of 8.5 ml per hour (SV=0.5/h). The liquid flowing out of thestainless steel tube was collected and analyzed by gas chromatography,and it was found that the conversion of dodecanedioic acid intododecanedioic acid dimethyl ester was 93.17%. The liquid wasconcentrated under reduced pressure, to obtain 11.14 g of a residue as acolorless solid. The water content of the residue was 0.1%.

The residue obtained as above was dissolved into 10 g of methanol, andthe solution was passed through said stainless steel tube by a fixeddelivery pump at a rate of 8.5 ml per hour (SV=0.5/h). The liquidflowing out of the stainless steel tube was collected and analyzed bygas chromatography, and it was found that the conversion ofdodecanedioic acid into dodecanedioic acid dimethyl ester was 99.21%.The liquid was concentrated under reduced pressure by a rotaryevaporator and dried by a vacuum dryer for 4 hours, to obtain 11.21 g ofa residue as a colorless solid. The residue was analyzed by gaschromatography, and it was found that the purity of dodecanedioic aciddimethyl ester was 99.25%. The yield of dodecanedioic acid dimethylester obtained from the purity was 99. 17%.

Comparative Example 1

A 200 ml three-neck flask with a reflux condenser was charged with 10 gof dodecanedioic acid, 80 g of methanol and 50 ml of the reproduced"Diaion" PK-220, and the mixture was stirred by a mechanical stirrerwhile being refluxed (64° C.) for 6 hours. The reaction solution wasanalyzed by gas chromatography, and it was found that the conversion ofdodecanedioic acid into dodecanedioic acid dimethyl ester was 99.17%.The reaction solution was filtered, and the obtained filtrate wasconcentrated under reduced pressure by a rotary evaporator and dried bya vacuum dryer for 4 hours, to obtain 11.21 g of a residue as acolorless solid. The residue was analyzed by gas chromatography, and itwas found that the purity of dodecanedioic acid dimethyl ester was99.16%. The yield of dodecanedioic acid dimethyl ester obtained from thepurity was 99.08%.

Comparative Example 2

A stainless steel tube with a diameter of 12 mm with a length of 200 mmopen at both the ends was packed with 17 ml of the reproduced "Diaion"PK-220, and placed in a 60° C. thermostatic oven.

A solution with 10 g of dodecanedioic acid dissolved in 80 g of methanolwas passed through said stainless steel tube at a rate of 7 ml per hour(SV=0.41/h). The liquid flowing out of the stainless steel tube wascollected and analyzed by gas chromatography, and it was found that theconversion of dodecanedioic acid into dodecanedioic acid dimethyl esterwas 99.11%. The liquid was concentrated under reduced pressure by arotary evaporator and dried by a vacuum dryer for 4 hours, to obtain11.21 g of a residue as a colorless solid. The residue was analyzed bygas chromatography, and it was found that the purity of dodecanedioicacid dimethyl ester was 99.07%. The yield of dodecanedioic acid dimethylester obtained from the purity was 98.99%.

Industrial applicability

According to the present invention, the amount of the alcohol used canbe decreased, and a highly pure alkanoic diacid dialkyl ester can beproduced at a high yield. The alkanoic diacid dialkyl esters producedaccording to the present invention can be suitably used as intermediatesof drugs, agricultural chemicals, perfumes, dyes, liquid crystalmaterials, high molecular materials, etc.

We claim:
 1. A method for producing an alkyl carboxylate, in which a carboxylic acid and an alcohol are esterified in a reaction solution in the presence of an acid catalyst, comprising the steps of partially completing the esterification reaction, interrupting the esterification reaction, removing water from said reaction solution while said esterification remains interrupted, said water removal being effected in one or more dehydration steps established during the esterification reaction, and restarting the esterification reaction by contact with acid catalyst to complete the esterification reaction.
 2. A method for producing an alkyl carboxylate, in which an alkanedioic acid and an alcohol are esterified by reaction in the presence of an acid catalyst, comprising the steps of interrupting the esterification reaction, removing water from the reaction solution by dehydration and restarting the esterification reaction to complete the esterification reaction.
 3. A method for producing an alkyl carboxylate, according to claim 1 or 2, wherein the dehydration step is established with the reaction solution kept away from contact with the acid catalyst.
 4. A method for producing an alkyl carboxylate, according to claim 1 or 2, wherein the dehydration is performed in one or more additional dehydration steps.
 5. A method for producing an alkyl carboxylate, according to claim 1 or 2, wherein in the dehydration step, water is removed until the water content of the reaction mixture becomes
 0. 5% or less after which the ester if i cat ion react ion is restarted.
 6. A method for producing an alkyl carboxylate, according to claim 2, wherein the acid catalyst is a solid acid catalyst.
 7. A method for producing an alkyl carboxylate, according to claim 1, wherein the solid acid catalyst is a strong acid ion exchange resin.
 8. A method for producing an alkyl carboxylate, according to claim 2, wherein the alkanedioic acid is represented by the general formula HOOC--X--COOH, where X stands for a straight chain, a branched chain or a cyclic alkyl chain having 6 to 14 carbon atoms.
 9. A method for producing an alkyl carboxylate, according to claim 1 or 2, wherein the alcohol is a monohydric alcohol.
 10. A method for producing an alkyl carboxylate, according to claim 9, wherein the monohydric alcohol is a straight chain or branched chain monohydric alcohol with 1 to 4 carbon atoms.
 11. A method for producing an alkyl carboxylate, according to claim 9, wherein the monohydric alcohol is a monohydric alcohol with a boiling point lower than that of water. 